HOUSTON (AFP) - Kevin Anderson survived a five-hour rain delay to clinch a berth in the semi-finals of the US Clay Court Championships with a gruelling 7-5, 6-7 (6-8), 7-6 (7-3) win over Jeremy Chardy.

The 28-year-old South African did not wrap up Friday's marathon quarter-final match until 11 hours after he stepped on court to face France's Chardy.

"They were incredibly tough conditions," Anderson said. "I could have made it a little easier on myself, but it's something I can improve on going into the next match.

"I have to give myself credit, I think I did a great job sticking it out."

Anderson now seeks to reach the 10th ATP Tour final of his career and his second this season when he faces world No. 46 Jack Sock, of the US, in the semis. He also made the final earlier this year in Memphis.

He served for the match at 5-4 in the second set before Chardy rallied to win the tie-breaker.

Anderson served for the victory again at 5-3 in the third set, only to get broken for a third time. He would need a deciding tiebreak to seal the match.

Sock followed up his upset victory over second seed Roberto Bautista Agut with a 6-4, 6-4 win over Santiago Giraldo.

It is the third time he has reached the semi-finals at an ATP event with each coming on a different surface, comprising the hard courts in Atlanta, grass in Newport and now clay courts in Houston.

American Sam Querrey defeated Spanish top seed Feliciano Lopez 6-4, 6-1 and Fernando Verdasco, of Spain, toppled the Russian Teimuraz Gabashvili 6-2, 6-3.

Querrey blasted seven aces in the 64-minute match as he makes his third appearance in the Houston semi-finals.